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ŠUMARSKI LIST 11-12/2012 str. 48     <-- 48 -->        PDF

Histiostomatidae are characterized by a short life cycle and can usually be easily cultured. This is why a wealth of biological data is permanently available. Astigmatid mites disperse as deutonymphs, which attach via a complex suckerplate to their phoretic carriers. They have no functional mouth. Adults are usually bacterial filter feeders (Wirth 2004). With about 500 named species, Histiostomatidae represent one of the largest groups within Astigmata. A number of histiostomatid species are known to be associated with bark beetles. Those from North America are Bonomoia pini Scheucher, 1957 and described by Woodring and Moser, 1970: Bonomoia certa, Histiostoma conjuncta, H.insolita, H. media, H. sordida and H. varia (Moser 1975). Those from Central-Europe are Bonomoia pini, Histiostoma piceae, H. trichophorum Oudemans, 1912, H. ulmi, H. crypturgi, H. gordius Vitzthum, 1923, H. vitzthumi, H. dryocoeti, H. oudemansi Womersley, 1941, H. pini, H. gladiger Vitzthum, 1926 and H. abietis (Scheucher 1957; Schwerdtfeger 1981; Pernek et al. 2012). They all are associated with different bark beetle species (Scheucher 1957). The European species have been considered a monophyletic group (Wirth 2004). Histiostoma ulmi Scheucher, 1957 is not phoretic on Scolytus beetles, but instead rides on the tenebrionid Hypophloeus bicolor Olivier, 1790 to the scolytid galleries (Scheucher, 1957).
Scheucher (1957) described several new species – Histio­stoma piceae, H. ulmi, H. crypturgi, H. dryocoeti, H. oudemansi, H. abietis, H. vitzthumi and H. pini – but type material of her species does not exist. Therefore, H. ulmi could only be determined using her drawings of deutonymphs and adults.
Galleries of bark beetles (Curculionidae, Scolytinae), are known to host a substantial biodiversity of mites (e.g. (Scheucher 1957; Lindquist 1969). Different groups of mites are often present, and mostly stay in phoretic association with their corresponding beetle species. They use the beetles as carriers from one habitat to a new one. Members of Gamasida, Trombidiformes, Oribatida and Astigmata can be found attached to beetles, as well as free living associates in the galleries (Pernek et al. 2012). Sometimes the relationships between organisms can be more complex, such as when fungi become involved in these phoretic interactions.
Mite communities associated with Cerambycidae are poorly studied. Mites belonging to the Histiostomatidae (Astigmata) are very rarely found associated with longhorn beetles. Scheucher (1957) assumed the histiostomatid mite B. pini to be (besides other carriers) phoretically associated with Acanthocinus aedilis Linnaeus, 1758.
Mite communities associated with bark beetles (Scolytinae) and biological data about those beetles – which often act as forest pests – are much better investigated. For example the southern pine beetle Dendroctonus frontalis Zimmermann, 1868 carries phoretic mites of the genus Tarsonemus (Trombidiformes), which possess special morphological adaptations for a hyperphoretic transfer of fungal spores (Ophiostomatide) termed sporathecae (Moser 1985; Klepzig et al. 2001; Hofstetter et al. 2006). Tarsonemus mites phoretic on D. frontalis transport the fungus Ophiostoma minus (Hedgcock) H. and P. Sydow, on which they feed, directly into the bark beetle galleries. Bridges and Moser (1986) found a positive relationship between the occurrence of bluestain fungus and Tarsonemus krantzi Smiley and Moser, 1974 mites in D. frontalis outbreaks. A related fungus, Ophiostoma novo-ulmi Brasier, 1991, responsible for Dutch elm disease, is a very important threat to Ulmus spp. trees across European forests, and may also be carried by Tarsonemus mites (Moser et al. 2010). Tarsonemus ips Lindquist, 1969 indirectly inhibits reproductive success of beetles through interactions with the antagonistic bluestain fungi O. minus (Lombardero et al. 2003).
The aim of the present paper is to describe a new finding of H. ulmi, a histiomatid mite formerly not known to inhabit cortical tissue galleries of the phloemophagous beetles Acanthocinus reticulatus Razoumov, 1789 and possibly Pityo­kteines curvidens Germar, 1824 and P. spinidens Reitter, 1894 of silver fir (Abies alba Mill.). Some ecological and morphological information about H. ulmi is additionally presented.
Materials and methods
Materijali i metode
Two silver fir trees were felled in March 2011 in a natural silver fir stand in Otočac (15°13´50˝E and 44°50´57˝N). In this way they were exposed for colonisation by bark and wood living insects during the spring-summer. Before being felled, trees in different condition of health were selected: i) T1 with still green needles and no sign of any vi­sible kind of infestation; ii) T2 characterized by red needles. The trunks were inspected in June and September. Small pieces of bark were cut out in order to identify the presence or absence of phloemophagous beetles. Two bolts of each tree were cut at levels of 10 m and 20 m per tree, each section was approximately 40 cm long, and 50 cm wide in diameter. They were brought into insect mesh covered cages in a climatic chamber and kept there at a humidity of 60 % and a constant room temperature of 20 °C and 16L:8D photoperiod. Sections were sprinkled daily with water to maintain optimal moisture in the bark.
Histiostomatid mites from those samples were cultured under conditions developed by Wirth and Moser (2010) as a standard method to rear species from their original substrate. Bark samples (2 square centimetres) were taken daily from the trees on September 12 until 29, 2011 using a knife.